1. Field of the Invention
The present invention relates to a method for evaluating or selecting an agent for preventing or curing photodamage of skin.
2. Description of the Invention
In the course of development of cutaneous photodamage, quantitative and qualitative changes are induced in both dermis and epidermis, in which such changes in dermis are especially known. That is, cells producing dermal fibers are reduced in size as well as in number due to chronic exposure to solar rays, which leads particularly to heavy loss of collagen fibers and results in degradation of the dermis and loss of subcutaneous adipose tissue. As a result, morphology of skin is changed due to decreased elasticity and looseness of skin, or increased roughness of skin surface.
In order to elucidate the mechanism of photodamage of the skin, or to evaluate a pharmaceutical product useful for the prevention and cure of adverse effects due to photodamage, a model system which can more satisfactorily reflect the photodamaged skin of human being will be useful.
As a skin model or animal model for photoaging, which is caused by photodamage, a system which is exposed to ultraviolet radiation is mostly generally used, and for example, methods of continuously irradiating the dorsal skin of a hairless mouse or the plantar skin of a rat, with ultraviolet radiation everyday for several weeks (Bissett D L, Hannon D P and Orr T V, Photochem. Photobiol., 46 (3), 367-78 (1987); Imayama S, Nakamura K, Takeuchi M, Hori Y, Takema Y, Sakaino Y and Imokawa G, J. Dermatol. Sci., 7 (1), 32-8 (1994) ) are known. However, it is considered more desirable to use human skin itself or grafted human skin which can also reflect the kinetics in the subcutaneous tissue.
As a model system utilizing human skin, a method of performing a single ultraviolet irradiation to a nude mouse (SCID mouse) having human skin grafted thereon is known (Del Bino S, Vioux C, Rossio-Pasquier P, Jomard A, Demarchez M, Asselineau D, Bernerd F, Br. J. Dermatol., 150 (4), 658-67 (2004)). However, since this is not a model in which ultraviolet radiation is continuously irradiated every day for several weeks, and involves ultraviolet irradiation for a short time period, the condition of photodamage in human skin under the effect of long-term irradiation of UVB cannot be sufficiently observed in the model. Thus, there has been established an animal model provided with a photodamaged human skin, which highly approximates photodamage, by continuously irradiating a specific amount of UVB for a specific amount of time (Hachiya A, et al., Am. J. Pathol., 174, 401 (2009)).
Meanwhile, matrix metalloproteinases (MMPs) are enzymes which degrade extracellular matrix proteins such as collagens, elastins and proteoglycans, and are reported to participate in the process of photodamage. It is reported, with regard to photodamaged skin, that disproportion of MMP-1 simultaneously causes loss of collagens I and III due to decreased synthesis of procollagens, as well as degradation of collagens in the dermis (Brennan M, et al., Photochem. Photobiol., 78, 43-48 (2003)). It is also reported that loss of collagens VII and IV at the dermal-epidermal junction is recognized in a skin where photodamage can be seen, and in the experiment using hairless mice, repeated irradiation of UVB induces production of MMP-2 and MMP-9, thus augmenting the degradation of collagens VII and IV (Contet-Audonneau J L, et al., Br. J. Dermatol. 140, 1038-1047 (1999)).
The activity of MMPs is known to be inhibited by tissue inhibitors of metalloproteinases (TIMPs), and a TIMP exhibits its inhibitory action by forming a 1:1 complex with an activated MMP. Therefore, normalizing the balance between the MMP activity and the TIMP activity is considered useful for the prevention of skin aging, and it has been found to date that, for example, an extract of cultured cells of a plant belonging to the genus Lithospermum and a caffeic acid polymer have an MMP inhibitory action (Japanese Patent Application Laid-Open (JP-A) No. 2008-31088). Currently, it is known that there are four types of the TIMPs, i.e., TIMP-1, TIMP-2, TIMP-3 and TIMP-4, and the above-mentioned patent document discloses that lithospermic acid has a TIMP-2 activity enhancing action.
JP-A No. 2000-86489 describes that combining retinol and sitosterol results in a decrease in the contents of MMP-1 and MMP-3 that are related to intrinsic aging, and an increase in the content of TIMP-1, but the data presented in the Examples do not necessarily show a decrease in the contents of MMP-1 and MMP-3 in connection with the aforementioned combination, and do not show an increase in the content of TIMP-1. Furthermore, this patent document is not related to photodamage.
In regard to TIMP-1, it has also been reported that a single irradiation of UVB increases the expression level of TIMP-1 mRNA (Brenneisen P, et al., Photochem. Photobiol., 64, 877-885 (1996)), while a single irradiation of UVB does not change the expression level of TIMP-1 protein (Brenneisen P, et al., Biochem. J., 365, 31-40 (2002)).
However, nothing has been known heretofore concerning the influence of the long-term irradiation of UVB on TIMP-1, and the relevance between photodamage of skin and TIMP-1 has not been investigated.